准噶尔盆地腹部侏罗系地层超压成因机制——以东道海子北凹陷为例

The mechanism of overpressure within the Jurassic formation in the central part of Junggar Basin： Dongdao Haizibei depression

准噶尔盆地腹部地区侏罗系地层超压普遍发育，超压层段与声波时差、电阻率两者之间具有较好的响应关系，尤以电阻率响应最为显著，超压层段声波时差表现为异常高值，电阻率为异常低值的特征。利用准噶尔盆地腹部地区大量测井、测试及相关地质资料综合论述超压成因，指出泥岩和砂岩中发育的超压并非由压实不均衡、构造挤压等作用导致，而主要由生烃作用造成的。研究表明有以下几方面主要证据：1）超压泥岩密度不具有异常低值特征；2）超压段泥岩密度与岩石颗粒垂直有效应力之间不存在线性关系；3）超压砂岩不存在异常高地温梯度现象；4）超压顶界面深度范围为3800—4300m，侏罗系烃源岩现今成熟度（Ro％）范围为0．6％-0．9％，温度范围分布在90℃-125℃；5）超压层段的侏罗系烃源岩现今生烃转化率最高可达70％，现今平均生油率可达90mg／g·TOC，仍具有较强的生烃能力；6）泥质烃源岩本身对超压具有很好的封闭作用；7）侏罗系烃源岩内发育大量低角度或高角度微裂缝；8）超压储层主要以油层为主，无水层，准噶尔盆地东道海子北凹陷砂岩中超压主要是通过烃源岩中排出的高压流体运移至储层发生超压传递的结果。

Overpressure is common in the Jurassic formation of the central part of Junggar Basin Overpressure layer has a better response relationship with interval transit time and resistivity, especially the resistivity response, which is characterized by abnormal high value of interval transit time and low resistivity of resistivity. In this paper, large numbers of well-logging, tests and geological data in the central part of Junggar Basin are used to determine the origin of overpressure. The author puts forward that the overpressure developed in the mudstone and sandstone is not caused by compaction and structural extrusion, but mainly by the effect of hydrocarbon generation. The result shows that there are several main evidences： 1） The overpressure mudstone density does not have abnormal low characteristic; 2） There is no linearrelationship between the density of overpressure segment and the vertical effective stress of rock particles; 3） There is no abnormal high ground temperature gradient phenomenon in overpressure sandstone; 4） The depths to the top of the overpressure range from 3 800 m to 4 300 m and the temperature for the top of overpressure zones is approximately 90 ℃- 125 ℃ , corresponding to an estimated vitrinite （Ro%） of 0.6%-0.9%; 5） The Jurassic hydrocarbon source rocks in the overpressure layer can reach up to 70% at present, and the average oil rate can reach 90 mg/g· TOC, and they still have strong hydrocarbon generation ability; 6） The clay source rock itself has a good sealing effect on overpressure; 7） There is a large number of low angle or high angle microfractures developed in Jurassic hydrocarbon source rocks; 8） The overpressure reservoir is mainly based on oil layer, without water layer. It concluded that the overpressure of sandstone is mainly the result of overpressure transmission from the overpressure source rock in Dongdao Haizibei depression of Junggar Basin.